1. Field of the Invention
This invention relates to an improved anti-reflective coating and a method for etching and removing an anti-reflective coating from a substrate. More specifically, this invention provides a plasma enhanced chemical vapor deposition dielectric anti-reflective coating and a method for etching and removing both a dielectric anti-reflective coating and a tungsten-silicide layer which supports the dielectric anti-reflective coating. The removal of the dielectric anti-reflective coating and the tungsten-silicide layer by etching is conducted for producing semiconductor integrated circuits containing transistors.
2. Description of the Prior Art
Since semiconductor devices were first introduced several decades ago, device geometries have decreased dramatically in size. During that time, integrated circuits have generally followed the two-year/half-size rule (often called xe2x80x9cMoore""s Lawxe2x80x9d), meaning that the number of devices which will fit on a chip doubles every two years. Today""s semiconductor fabrication plants routinely produce devices with feature sizes of 0.5 microns or even 0.35 microns, and tomorrow""s plants will be producing devices with even smaller feature sizes.
A common step in the fabrication of such devices is the formation of a patterned thin film on a substrate. These films are often formed by etching away portions of a deposited blanket layer. Modern substrate processing systems employ photolithographic techniques to pattern layers. Typically, conventional photolithographic techniques first deposit photoresist or other light-sensitive material over the layer being processed. A photomask (also known simply as a mask) having transparent and opaque regions which embody the desired pattern is then positioned over the photoresist. When the mask is exposed to light, the transparent portions allow for the exposure of the photoresist in those regions, but not in the regions where the mask is opaque. The light causes a chemical reaction in exposed portions of the photoresist. A suitable chemical, chemical vapor or ion bombardment process is then used to selectively attack either the reacted or unreacted portions of the photoresist. With the remaining photoresist pattern acting as a mask, the underlying layer may then undergo further processing. For example, the layer may be doped or etched, or other processing may be carried out.
When patterning such thin films, it is desirable that fluctuations in line width and other critical dimensions be minimized. Errors in these dimensions can result in variations in device characteristics or open-/short-circuited devices, thereby adversely affecting device yield. Thus, as feature sizes decrease, structures must be fabricated with greater accuracy. As a result, some manufacturers now require that variations in the dimensional accuracy of patterning operations be held to within 5 percent of the dimensions specified by the designer.
Modern photolithographic techniques often involve the use of equipment known as steppers, which are used to mask and expose photoresist layers. Steppers often use monochromatic (single-wavelength) light, enabling them to produce the detailed patterns required in the fabrication of fine geometry devices. As a substrate is processed, however, the topology of the substrate""s upper surface becomes progressively less planar. This uneven topology can cause reflection and refraction of the monochromatic light, resulting in exposure of some of the photoresist beneath the opaque portions of the mask. As a result, this uneven surface topology can alter the mask pattern transferred to the photoresist layer, thereby altering the desired dimensions of the structures subsequently fabricated.
When a photoresist layer is deposited on a reflective underlying layer and exposed to monochromatic radiation (e.g., deep ultraviolet (UV) light), standing waves may be produced within the photoresist layer. In such a situation, the reflected light interferes with the incident light and causes a periodic variation in light intensity within the photoresist layer in the vertical direction. Standing-wave effects are usually more pronounced at the deep UV wavelengths used in modern steppers than at longer wavelengths because the surfaces of certain materials (e.g., oxide, nitride and polysilicon) tend to be more reflective at deep UV wavelengths. The existence of standing waves in the photoresist layer during exposure causes roughness in the vertical walls formed when sections of the photoresist layer are removed during patterning, which translates into variations in linewidths, spacing and other critical dimensions.
One technique helpful in achieving the necessary dimensional accuracy is the use of an antireflective coating (ARC). An ARC""s optical characteristics are such that reflections occurring at inter-layer interfaces are minimized. The ARC""s absorptive index is such that the amount of monochromatic light transmitted (in either direction) is minimized, thus attenuating both transmitted incident light and reflections thereof. The ARC""s refractive and reflective indexes are fixed at values that cause any reflections which might still occur to be canceled.
As integrated circuit critical dimensions (CDs) shrink below 0.35 micron, the use of shorter wavelengths for photolithography imaging is required. For sub-0.35 micron critical dimensions, the wavelength for stepper tools has dropped into the deep ultraviolet (248 nm) range. One trade-off of the shorter wavelength is that the reflectivity from the substrate interface increases due to interference effects. Additionally, the shorter wavelength increases standing wave effects in the resist. The combination of interference and standing waves can greatly reduce CD control over various surface topographies.
The use of conventional ARC layers has successfully enhanced CD control for various polysilicon and silicided gate structures. However, one common phenomenon with conventional ARC films, especially spin-on organic ARC films, and deep-UV applications is a xe2x80x9cresist footingxe2x80x9d which has been observed at the resist/ARC interface. This phenomenon is attributed to the reactive nature inherent in deep-UV resists such as Apex-E(copyright), a registered trademark of Shiply Corporation. The photoresist sensitivity to the underlying surface may cause the resist to incompletely activate, thereby leaving a xe2x80x9cfootxe2x80x9d at the bottom corners of the imaged line and resulting in CD variation. Another problem with conventional ARC layers is that one type of etchant gas has to be used to etch and open up the ARC while another type of etchant gas must be used to etch the underlying layer(s) supporting the ARC. Thus, there are a number of process steps needed in the etch recipe.
Therefore, what is needed and what has been invented is an improved ARC film, more specifically an improved dielectric ARC film, for deep-UV lithography on tungsten silicide (WSix) and polysilicon films without the xe2x80x9cresist footingxe2x80x9d phenomena. What is further needed and what has been invented is a method for etching a dielectric ARC with an etchant gas that may be subsequently used to etch the underlying layer(s) that supports the dielectric ARC. What is yet further needed and what has been invented is an etchant gas for the removal of a dielectric ARC from a substrate.
To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention is embodied in a method and apparatus for etching dielectric layers and inorganic ARCs without the need for removing the substrate being processed from the processing chamber and without the need for intervening processing steps such as chamber cleaning operations. This process is thus referred to herein as an in situ process.
The present invention is further embodied in a process for etching a layer and/or a multi-layer film deposited on a substrate, such as silicon, located within a processing chamber. The substrate has a base, an underlying layer above the base, an overlying layer above the underlying layer, and a top dielectric (DARC) layer formed on the overlying layer. In a preferred embodiment, first the DARC layer and the overlying layer, such as silicide (WSix), is etched by a first process gas. Next, the underlying layer, such as a polysilicon layer, is etched by a second process gas. These steps are performed as an in situ process. In another embodiment, first the DARC layer is etched by a first process gas. Second, the overlying layer, such as a silicide (WSix), is etched by a second process gas. Next, the underlying layer, such as a polysilicon layer, is etched by a third process gas. These steps are also performed as an in situ process.
Throughout both processes the substrate remains in the processing chamber. Accordingly, the present invention eliminates the need to remove the substrate from the processing chamber between etching of the different layers, for chamber cleanings and the like. This improves throughput, reduces downtime and reduces contamination, among other benefits. In addition, the in situ processes of the present invention allow accurate control over the etch rate of the layers.
A feature of the present invention is the ability to etch a dielectric ARC with high etch selectivity. Another feature of the present invention is the capability of in situ etching of dielectric layers and inorganic ARCs. An advantage of present invention is that accurate etching of the DARC layer is produced. Another advantage of present invention is that the substrate being processed does not need to be removed from the processing chamber. Yet another advantage of present invention is that unwanted etching of layers underlying the layer being patterned is avoided. Another advantage of the present invention is that it can be used for all work related to etching, such as metal and silicon etching.
The present invention therefore accomplishes its desired objects by broadly providing a method for removing an anti-reflective coating from a substrate comprising the steps of:
a) providing a substrate supporting an anti-reflective coating;
b) providing an etchant gas comprising a fluorine-containing gas (e.g., NF3) and a halogen-containing gas (e.g., Cl2); and
c) etching the anti-reflective coating of step (a) with the etchant gas of step (b) to remove the anti-reflective coating from the substrate.
The present invention also accomplishes its desired objects by broadly providing a method for etching a tungsten-silicide layer supporting an anti-reflective coating comprising the steps of:
a) providing a substrate supporting a tungsten-silicide layer having an anti-reflective coating disposed thereon;
b) providing an etchant gas comprising NF3 and Cl2;
c) etching the anti-reflective coating of step (a) with the etchant gas of step (b) to remove at least a portion of the anti-reflective coating to expose at least part of the tungsten-silicide layer; and
d) etching the exposed part of the tungsten-silicide layer with the etchant gas of step (b).
The anti-reflective coating is a dielectric anti-reflective coating having the formula SiOxNyHz wherein x is from 1 to 2 and y is from 0 to 1. Preferably, the anti-reflective coating is SiON. The etchant gas preferably comprises from about 10% by vol. to about 50% by vol. NF3 and from about 50% by vol. to about 90% by vol. Cl2. Preferably, the etchant gas consists of or consists essentially of NF3 and Cl2. The anti-reflective coating may support a mask layer (e.g., tetraethylorthosilicate) which would be etched and removed prior to etching the anti-reflective coating. The method for removing an anti-reflective coating additionally comprises disposing, prior to etching the anti-reflective coating, the substrate in a high density plasma chamber including a coil inductor and wafer pedestal; and performing the etching of the anti-reflective coating in the high density plasma chamber under the following process conditions:
The present invention further accomplishes its desired objects by broadly providing a method for producing a dielectric anti-reflective coating gate structure comprising the steps of:
a) forming a patterned resist layer, a mask layer, a dielectric anti-reflective coating, and at least one conductive layer on a substrate;
b) etching a portion of the mask layer to remove the portion of the mask layer from the dielectric anti-reflective coating to produce the substrate supporting the patterned resist layer, a residual mask layer, the dielectric anti-reflective coating, and the at least one conductive layer;
c) etching the dielectric anti-reflective coating of step (b) with an etchant gas comprising NF3 and Cl2 to produce the substrate supporting the patterned resist layer, the residual mask layer, a residual dielectric anti-reflective coating, and the at least one conductive layer; and
d) etching the at least one conductive layer with the etchant gas of step (c) to produce a dielectric anti-reflective coating gate structure.
As previously indicated, the dielectric anti-reflective coating preferably has the formula SiOxNyH wherein x is an integer having a value ranging from 1 to 2 and y is an integer having a value ranging from 0 to 1. More preferably, the dielectric anti-reflective coating is SiON. The mask layer preferably comprises tetraethylorthosilicate. The at least one conductive layer preferably comprises tungsten silicide (WSix), more preferably a layer of a polysilicon layer supporting a tungsten silicide layer. As also previously indicated, the etchant gas flows at a rate ranging from about 100 sccm to about 200 sccm and preferably consists of or consists essentially of NF3 and CL2. The method for producing a dielectric anti-reflective coating gate structure additionally comprises disposing, prior to the etching step (c), the substrate of step (b) in a high density plasma chamber including a coil inductor and a wafer pedestal; and performing the etching step (c) and the etching step (d) in the high density plasma chamber under the following process conditions:
It is therefore an object of the present invention to provide a method for removing an anti-reflective coating from a substrate.
It is another object of the present invention to provide a method for etching a tungsten-silicide layer supporting an anti-reflective coating.
It is yet another object of the present invention to provide a method for producing a dielectric anti-reflective coating gate structure, and to provide a dielectric anti-reflective coating gate structure produced in accordance with the method(s) of the present invention.
These, together with the various ancillary objects and features which will become apparent to those skilled in the art as the following description proceeds, are attained by these novel methods, a preferred embodiment thereof shown with reference to the accompanying drawings, by way of example only, wherein: